'use strict';

const PERSIAN_WEEKDAYS = ['یکشنبه', 'دوشنبه', 'سه‌شنبه', 'چهارشنبه', 'پنجشنبه', 'جمعه', 'شنبه'];
const IRAN_WEEK_ORDER = [6, 0, 1, 2, 3, 4, 5];

const toDate = (value) => {
  if (!value) return null;
  const date = value instanceof Date ? value : new Date(value);
  return Number.isNaN(date.getTime()) ? null : date;
};

const formatClockPart = (time) => {
  const raw = String(time || '').trim();
  if (!raw) return '';
  const [hoursRaw, minutesRaw] = raw.split(':');
  const hours = String(parseInt(hoursRaw, 10));
  if (hours === 'NaN') return '';
  if (!minutesRaw || minutesRaw === '00') return hours;
  return `${hours}:${minutesRaw}`;
};

const formatCourseTime = (startTime, endTime) => {
  const start = formatClockPart(startTime);
  const end = formatClockPart(endTime);
  if (!start) return '';
  if (!end) return start;
  return `از ${start} تا ${end}`;
};

const weekdayIndex = (value) => {
  const date = toDate(value);
  return date ? date.getDay() : null;
};

const joinFaList = (items) => {
  if (!items.length) return '';
  if (items.length === 1) return items[0];
  if (items.length === 2) return `${items[0]} و ${items[1]}`;
  return `${items.slice(0, -1).join('، ')} و ${items[items.length - 1]}`;
};

const formatClassDays = (sessions = []) => {
  const indexes = [];
  const seen = new Set();
  for (const session of sessions) {
    const dayIndex = weekdayIndex(session?.day);
    if (dayIndex == null || seen.has(dayIndex)) continue;
    seen.add(dayIndex);
    indexes.push(dayIndex);
  }
  indexes.sort((a, b) => IRAN_WEEK_ORDER.indexOf(a) - IRAN_WEEK_ORDER.indexOf(b));
  return joinFaList(indexes.map((index) => PERSIAN_WEEKDAYS[index]).filter(Boolean));
};

const formatClassStartDate = (value) => {
  const date = toDate(value);
  if (!date) return '';
  try {
    return date.toLocaleDateString('fa-IR');
  } catch {
    return date.toISOString().slice(0, 10);
  }
};

const buildClassScheduleContext = (classDoc, sessions = [], currentSession = null) => {
  const sortedSessions = [...sessions].sort((a, b) => {
    const left = toDate(a?.day)?.getTime() || 0;
    const right = toDate(b?.day)?.getTime() || 0;
    return left - right;
  });
  const sessionForTime = currentSession || sortedSessions[0] || null;

  return {
    classStartDate: formatClassStartDate(classDoc?.startDate || sortedSessions[0]?.day),
    classDays: formatClassDays(sortedSessions),
    courseTime: formatCourseTime(sessionForTime?.startTime, sessionForTime?.endTime)
  };
};

module.exports = {
  formatCourseTime,
  formatClassDays,
  formatClassStartDate,
  buildClassScheduleContext
};